1. Field of the Invention
The present invention relates to an optical disc drive for recording/reproducing device, and more particularly, to an optical pick-up actuator and methods thereof.
2. Background of the Related Art
An apparatus for reproducing a recorded signal stored in an optical disc is called an optical disc drive. Such an optical disc drive has an optical pick-up unit and an object lens driving unit for allowing a light spot to trace a center of a signal track of the optical disc such that an influence of a surface vibration and an eccentricity, etc. of the optical disc depending on a rotation of the optical disc is reduced or minimized on a light beam condensed from the object lens. Such an object lens driving unit is called an optical pick-up actuator. The object lens driving unit allows an activating unit (hereafter “lens holder”) having the object lens mounted thereon to move up/down, left/right, etc., to perform a servo function such as focusing and tracking, etc. of the beam condensed on an information recording surface of the optical disc.
Further, in the optical pick-up actuator of the optical disc drive used in a portable personal computer such as a notebook should be manufactured to be as thin and as light as possible for satisfying specifications such as a space limit and a hand convenience. In particular, since an interval between a reflective mirror and the object lens of the optical disc drive is a main element for determining a total height of the optical disc drive or the optical pick-up actuator, a structure for reducing the interval is required. In order to satisfy this requirement specification, a configuration of a front-protrusion-typed object lens is required for the slim-type optical pick-up actuator.
A related art slim-type optical pick-up actuator will be described as follows. As shown in FIGS. 1 and 2, the related art slim-type optical pick-up actuator 100 includes an object lens 101 mounted in a protrusion type on one side front surface of a lens holder 102, a focusing coil 103 wound along a circumference surface of a bobbin 110 having a first housing groove 102a formed at a center of the lens holder 102, and a tracking coil 104 wound at left/right portions of one side of the focusing coil 103.
Additionally, a pick-up base 106 has U-shaped yokes 106a protruded therefrom, and magnets 105 are attached to the one lateral surfaces (facing surfaces) of the protruded yokes 106a. Such magnets 105 and yokes 106a are respectively protruded toward the first housing groove 102a and a second housing groove 102b such that the magnets 105 face each other.
In the pick-up base 106, a support 106b spaced a predetermined distance away from the yoke 106a, a frame 109, and a circuit substrate 108 attached to a rear surface of the frame are combined and fixed using a screw 120 and screw holes 108a and 106c. Additionally, the lens holder 102 is supported by a pair of wire suspensions 107 connected between the frame 109 and a substrate 111 fixed to a central portion of both lateral surfaces of the lens holder.
The focusing coil 103 is installed around a circumference surface of the second housing groove 102b, and the tracking coil 104 is installed at both front sides of the focusing coil 103. A single groove formed in an internal section of the lens holder 102 is divided into the first and second housing grooves 102a and 102b by the bobbin 110 around which the focusing coil 103 and the tracking coil 104 are wound.
One side portion of each of the tracking coil 104 is positioned between the magnets 105. Further, each tracking coil 104 faces left/right sides of the magnets 105 facing each other.
In this structure, if a current is applied to the focusing coil 103 and the tracking coil 104, the focusing and tracking coils 103 and 104 each are subjected to the force of the electromagnetic interaction of the focusing and tracking coils 103 and 104 and the magnets 105 to move together with the lens holder 102. The focusing coil 103 and the tracking coil 104 are subjected to the force of the interaction with the magnet in a direction following the Fleming's left-hand rule.
At this time, if the interaction of the focusing and tracking coils 103 and 104 and the magnet 105 allows an electromagnetic force to be applied to the focusing and tracking coils 103 and 104, the bobbin 110 moves, together with the lens holder 102, in a focusing direction (Z) and a tracking direction (Y). The object lens 101 protruded at one side of the lens holder 102 is moved to control the position where the light spot is focused on the optical disc (not shown).
As shown in FIGS. 2 and 3, the mass center position (G) of the lens holder 102 using the above-described magnetic circuit structure is positioned between each tracking coil 104 and focusing coil 103. At this time, an operation center position (C1) of the first focusing coil 103a positioned between two magnets 105 is formed at an intersection point of a center of left/right sides of a first focusing coil 103a and a center of a coil thickness, and an operation center position (C2) of the tracking coil 104 is formed at an intersection point of a center of left/right-side tracking coils and a center of a coil thickness. Accordingly, the operation center positions (C1, C2) of each of the focusing and tracking coils 103a and 104 are positioned at different points. This is caused by a structure having the focusing coil 103 passing between two magnets 105 and having the tracking coil 104 at one external (e.g., both left/right) side of the focusing coil 103.
Additionally, the mass center position (G) of the lens holder 102 including the bobbin 110 having the coils 103 and 104 installed is designed to be positioned between the operation center positions (C1, C2) of the focusing and tracking coils 103a and 104. Generally, a consistency of the operation center positions (C1, C2) of the coils 103a and 104 with the mass center position (G) at one position would allow the actuator to perform in its best or optimal operation state. When the mass center position (G) is in a non-consistent state with both the operation center positions (C1, C2) of the coils 103a and 104, but is allowed to be consistent with only one operation center position, an operation characteristic of the coil is deteriorated.
Accordingly the mass center position (G) is designed to be positioned between the operation center positions (C1, C2) of the coils 103a and 104. However, even in this case, since the mass center position (e.g., a movement center position (G)) of the lens holder 102 is not consistent, there is a drawback in that the lens holder 102 moves in a slant (e.g., not exactly in the Y and Z directions), at the time of a focusing or tracking operation. Further, the operation center position of the second focusing coil 103b (C3) is positioned at an opposite side of the focusing coil 103. Since a leakage flux of these portions (C3, 103b ) is positioned at a rear surface of the magnet 105, it acts with a force in an opposite direction to the focusing operation.
FIGS. 4a and 4b are diagrams showing distribution views of a magnetic flux density and a vector of the coil in the optical pick-up actuator of FIG. 1. As shown in FIG. 4a, if the current is applied to the focusing coil 103, the flux density of the focusing coil 103 has an unbalanced distribution. That is, the first focusing coil 103a portion between the magnets 105 has the magnetic flux concentrated by the interaction of the magnet 105, but since the second focusing coil 103b portion at the rear surface of the yoke is blocked by the yoke 106a, it is not affected by the magnet 105.
FIG. 4b is a view illustrating a flux distribution and a vector distribution of a related art tracking coil. Since the tracking coil 104 is disposed at the left/right sides of the magnet 105, the magnetic flux is concentrated in a central direction of the magnet 105.
As shown in FIG. 5, the first focusing coil 103a at an inner side of the yoke 106a is subjected to the electromagnetic force caused by the interaction with the magnet 105, while the second focusing coil 103b at an outer side of the yoke 106a is blocked by the yoke 106a and is less affected or not affected by the magnet 105. Further, as shown in FIG. 5, the magnetic force line by the magnet 105 is less deviated from a center of the magnet 105 while it is widely spread at an edge of the magnet 105. Meanwhile, the magnetic force line is deviated from the yoke 106a to leak outside. The second focusing coil 103b positioned outside of the yoke 106a is affected by this leakage flux.
As shown in FIG. 5, an arrow coming from the focusing coil 103 illustrates a magnitude and a direction of the force applied to the focusing coil 103 according to a distribution of the magnetic force line by the Fleming's left-hand rule. As described above, even the outside second focusing coil 103b is subjected to the force by the affection of the leakage flux, and with respect to the total force from the focusing coil 103, this causes an unbalanced distribution of the force. That is, as shown in FIG. 6, a force (Fu) applied to the first focusing coil 103a positioned inside of the yoke 106a and a force (Fd) applied to the second focusing coil 103b positioned outside of the yoke 106a are unbalanced. Accordingly, a pitching mode (shown in FIG. 10a) occurs in which the bobbin 110 and the lens holder 102 yaw front and rear. That is, the bobbin 110 and the lens holder 102 are yawed in a direction of an arrow (P) of FIG. 6.
Further, the outside second focusing coil 103b is not used for a focusing operation, and a sensitivity of the optical pick-up actuator is reduced by a mass increase and a resistance increase of the wound coil. Accordingly, it impedes a high speed following capacity depending on a high-multiple speed of the disc.
On the other hand, at the time of movement of the left/right tracking coils 104 depending on a track direction (A), since the movement center position and the mass center position (G) are not consistent with each other, a rolling mode (shown in FIG. 10b) occurs. As shown in FIG. 7, when the bobbin 110 is in a stop state, a total mass center position (G) of the optical pick-up actuator 100 and the movement center position (H) of the bobbin 110 are consistent with each other. Arrows of the drawings illustrates the magnitude and the direction of the force applied to the tracking coil 104 by the magnet 105. The magnitude of the force applied to the tracking coil 104 depends on the magnitude of the magnetic flux and the current flowing through the tracking coil 104, and depends on only the magnitude of the magnetic flux in case the current is constant. Thus, the magnetic flux is the largest at the central portion of the magnet 105, and gradually becomes smaller at an outside edge thereof. Again, as shown in FIG. 7, when the tracking coil 104 is at a neutral position, since the magnetic flux is symmetrically distributed centering on the tracking coil 104, the mass center position (G) and the movement center position (H) of the tracking coil are allowed to be consistent with each other.
However, as shown in FIG. 8, if the bobbin 110 is focused upward by the focusing coil 103, the force applied to the tracking coil 104 by the magnet 105 is deflected downward of the tracking coil 104. Accordingly, since the downward tracking force of the bobbin 110 is larger than the upward tracking force thereof, the rotation moment is generated in an arrowed direction (R1). To the contrary, as shown in FIG. 9, if the bobbin is downward-focused by the focusing coil 103, the force applied to the tracking coil 104 by the magnet 105 is deflected upward of the tracking coil 104. Accordingly, since the tracking force upward of the bobbin 110 is larger than the tracking force downward thereof, the rotation moment is generated in an arrowed direction (R2). As a result, according to the focusing operation of the bobbin 110, the movement center position (H) of the tracking coil 104 is not allowed to be consistent with the mass center position (G), which results in the rolling mode (shown in FIG. 10b) rolling in the arrowed directions (R1, R2).
In the related art lens holder 102, a frequency characteristic of the optical pick-up actuator is determined by a rigidity of the wire suspension 107, which is installed at both sides. But, since the lens holder itself is an apparatus structure, it has a vibration frequency, and when the optical pick-up actuator is vibration-added at the vibration frequency, it is resonant in a proper vibration mode of the lens holder 102.
In related art optical pick-up actuator having the lens holder, the lens holder structure is vibrated to have a twisted or bent shape in a mode in which a total of the lens holder is transformed. In the related art lens holder, the focusing operation or the tracking operation should be completed before an initial transformation frequency of 17.2 KHz, and therefore, at a high-multiple speed of reproduction, a focusing or tracking control becomes difficult. Since this type of vibration mode in the lens holder causes the object lens to be vibrated at the same time, the beam is directly influenced such that it is difficult to control the actuator, which should follow the disc.
In addition, the proper vibration mode of the lens holder 102 is a characteristic, which is determined by a shape of the lens holder 102. The object lens 101 is vibrated together by the vibration mode of the lens holder itself. Accordingly, since the beam is distorted, a control characteristic of following the disc is badly affected.
As described above in the related art structure, a rotation vibration mode such as the pitching mode and the rolling mode in the actuator can affect a phase and a variation of a basic frequency characteristic at the time of the focusing and tracking operations, and accordingly, a degradation of the optical signal is caused. If the magnitude of the magnet 105 is increased to increase the flux density for improving an alternate current sensitivity, since the leakage flux is also increased together thereby resulting in a sub-resonance. Thus, there has been a limit in increasing the flux density. Furthermore, in the high-multiple speed and high density of optical recording and reproducing device, a pitching mode and rolling mode phenomenon can more seriously occur, and a degradation of the optical signal is caused.
In addition, the related art optical pick-up actuator has a drawback because when a high-dimensional resonant frequency is included in a high-pass frequency range, as the bobbin is transformed, the object lens is transformed or a position of the object lens is also changed in the bobbin to thereby cause the disc not to be exactly focused. Accordingly, the track signal of the disc is not exactly read out to thereby cause reproduction to be degraded or impossible.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.